Heat not burn products, which are sometimes also referred to as non-combustion type smoking articles, are being developed as a possible alternative to conventional smoking articles such as cigarettes. The basic principle is that the product heats tobacco to cause the volatilisation of the low boiling point components but avoiding pyrolysis or combustion of the tobacco or volatiles (although some charring of the tobacco can occur during normal usage). This volatilisation leads to the creation of a vapour which is drawn through the product and is then condensed into an aerosol and inhaled by the user. The volatilised components include water, nicotine, humectants and light volatiles.
The present invention relates in particular to those heat not burn products which include a heat source and an aerosol generating portion, such as a tobacco rod, from which certain components are vaporised during use. In such products the heat source may be a solid extrusion moulded article of a carbonaceous material which is lit to provide the heat for volatilisation and, following lighting, continues to smoulder and generate heat. In order to avoid burning on contact with the lit heat source, this part of the product may be surrounded by a non-flammable material such as fibreglass, a paper sheet containing glass fibres, a ceramic, or a paper sheet internally lined with a metal foil. The heat not burn products also include an aerosol-generating portion adjacent to the heat source. This portion generally has a cylindrical body similar in external appearance to the tobacco rod of a conventional cigarette. It includes components which are to be volatilised during use. This portion may include tobacco and will often comprise distinct sections having different functions, including a vaporisation chamber (for example comprising tobacco and an aerosol generating agent) adjacent to the heat source, and a cooling chamber (for example comprising shredded reconstituted tobacco sheet) further downstream towards the mouth end of the product. A filter or mouthpiece is usually situated at the mouth end of the product and this may comprise, for example, cellulose acetate.
These heat not burn products include aerosol generating agents such as propylene glycol (PG) and glycerol.
One of the primary aims of the heat not burn products is to earn consumer acceptance as an alternative to conventional smoking articles. One approach to achieving this acceptance will depend upon the heat not burn product producing a similar experience to the smoking articles (although it is recognised that it may also or alternatively be possible to achieve acceptance by other means).
An aspect of the experience of smoking a conventional smoking article is the so-called “puff profile”, also referred to as the “puff per puff profile”. This is the amount of total particulate matter yield (mg/cig) in each puff as the smoking article is consumed. The total particulate matter (TPM) delivery of a conventional cigarette is relatively low during the first couple of puffs, but it tends to gradually increase right through to the final puffs. This gives the smoker the sensation of the smoke gradually increasing in strength.
In contrast, for heat not burn products, the puff profile tends to start very weakly before rapidly increasing within the first few puffs. The TPM delivery then decreases until the product is consumed. This is mainly because these products take a few puffs to reach an optimum temperature, after which they give a high yield of aerosol. However, the puff yield can rapidly diminish during usage as the available aerosol generating agent, such as PG, is boiled off and used up. As a result, such heat not burn products are known to have the disadvantage that they tend to have diminished sensory properties towards the end of the product when compared with a conventional cigarette (see FIG. 1).
It is therefore an aim of the present invention to modify the puff profile of heat not burn products, for example, so as to produce a profile which more closely resembles that of a conventional smoking article.
It has been discovered that, although the aerosol generating agents are vaporised during use of the heat not burn product, vaporisation of some agents at lower temperatures can cause problems during storage of the products. Specifically, some aerosol generating agents can migrate during storage and subsequently be lost to the atmosphere or interact with other parts of the product such as the surrounding paper wrapper. This may also lead to staining or marking of the product, either by the agent itself or by compounds released from the agent interaction. It is therefore desirable to immobilize the aerosol generating agent within the heat not burn product until it is required.
Furthermore, when aerosol generating agents are included in heat not burn products, there is currently no way of controlling their vaporisation and therefore their effect on the puff profile of the product.
The present invention seeks to improve the performance of heat not burn products and overcome the aforementioned problems by controlling the release of aerosol generating agents.